At present, an X-ray inspection is used for a wide range of industrial products. The X-ray inspection is used also for a printed circuit board on which various electronic components are mounted. For example, an inspection, as to whether or not a BGA (Ball Grid Array), which is an ultra-small LSI component, is properly soldered to a board is made using X-rays. Generally, the BGA includes a solder ball terminal on an electrode pad thereof and is held in a state where the solder ball terminal is held in contact with a solder layer formed on a board-side electrode pad and, subsequently, a heating process is applied to melt solder balls (and the solder layer) to fix the BGA to the board. In the X-ray inspection, data on cross-sectional shapes of the melted solder balls is obtained. This is because the solder ball is deformed into a barrel shape by the heating process in a normal state, whereas it is deformed into a shape different from the barrel shape in a defective state.
An X-ray CT (Computed Tomography) method is known as an X-ray inspection method aimed at boards as described above. For example, Japanese Patent Publication No. 3665294 discloses an X-ray inspection method utilizing vertical slice imaging. In this inspection method, a multitude of horizontal slice images of a melt of the solder ball are imaged and a vertical slice image of the melt of the solder ball is formed utilizing these. However, this method requires several tens of X-ray images to be obtained for one inspection target, wherefore there are problems that it takes time for an imaging operation and an X-ray exposure dose of an inspection target increases.
Further, Japanese Unexamined Patent Publication No. 2010-127810 discloses an X-ray inspection method for obtaining a three-dimensional X-ray CT image by iteration using a plurality of X-ray sources and X-ray detectors. According to this method, a three-dimensional shape of an inspection target can be obtained, but an enormous number of X-ray images are necessary. Thus, an imaging time and an X-ray exposure dose of the inspection target are a problem similarly to the above case.